Effects of Hydrous Alteration on the Distribution of Base Metals and Platinum Group Elements within the Kevitsa Magmatic Nickel Sulphide Deposit, Finland

Platinum group Elements (PGE) and nickel are commonly assumed to be immobile in most conditions, especially during low temperature hydrothermal alteration. However, only a small number of studies have rigorously tested this assumption. The Kevitsa intrusion, northern Finland, provides a natural laboratory to study the behaviour of base metals and platinum group elements (PGE) during low temperature alteration. This 2.06 Ma mafic-ultramafic intrusion, located in the Central Lapland greenstone belt, which hosts disseminated Ni-Cu-(PGE) sulphide mineralisation, is affected by three types of alteration (amphibole, serpentinite and epidote-rich) and is cross cut by various types of veins. The effect of the circulation of hydrothermal fluids on the distribution of base metals and PGE was studied at two different scales. Interrogation of an extensive deposit-wide assay database provided information at the deposit-scale (kilometre scale), and a detailed study, involving laboratory, portable X-ray fluorescence analyses, and micro-XRF mapping provided information on the small scale (centimetre to decimetre scale) remobilisation of base metals and PGE. Results show that the hydration and carbonation of the Kevitsa mineralised mafic-ultramafic intrusion did not significantly affect the distribution of Ni and PGE at scales larger than a few mm, and that Cu and Au are the only metals that are affected by small to large scale remobilisation from centimetre to kilometre scale.